The present invention relates to methods for making curved or straight segments of polymeric devices which comprise nested tubing of varying physical and mechanical characteristics.
Since minimally invasive surgical procedures which use an endoscopic approach are now widely used in many surgical specialties, including cardiothoracic surgery, new surgical techniques and instruments have been developed especially to assist in minimally invasive coronary artery bypass grafting (CABG) surgeries. Devices having multiple lumens and ports can be used to deliver fluid and introduce instruments, such as pressure monitors, aspirators, or filters.
Techniques used to create a cannula or catheter having multiple lumens and shapes generally include adhesive bonding, injection or compression molding, casting and machining of devices. The traditional techniques are plagued by the following problems: (1) filling tubing with adhesives is difficult to control and inconsistent, creating yield losses and quality problems, (2) injection or compression molding requires costly tooling and cannot form specific shapes, and (3) machining is labor-intensive and cannot form certain shapes. A need therefore exists for methods which provide easy and consistent means of forming cannulas or catheters which have multi-layered tubing cross-sections, and for the resulting devices.
The present invention provides a nested tubing cannula, which has multi-layered tubing cross-sections. In minimally invasive CABG surgery, the cannula may function as a balloon occluder for aortic occlusion and a conduit for cardioplegia delivery or blood delivery from cardiopulmonary bypass (CPB) machine. The cannula comprises two elongate tubular members, which both have a proximal end, a distal end, and a lumen therebetween. One tubular member (the inner tubular member) has a diameter smaller than the other (the outer tubular member). The smaller tubular member is nested substantially coaxially within the lumen of the larger tubular member, so that the gap between the larger tubular member and the smaller tubular member defines one lumen, whereas another lumen is provided by the lumen of the smaller tubular member. A tubular sleeve may be disposed coaxially between the smaller and larger tubular members. In certain embodiments, the inner tubular member will be fitted with a beading or plug occluding and sealing the distal opening of its lumen. In an alternative embodiment, the distal end of the cannula may be angulated (e.g., at approximately 90xc2x0) relative to its proximal end for better positioning within a vessel wall.
Where the cannula comprises a balloon occluder, an elastomeric balloon with an inflatable chamber is mounted on the distal region of the outer tubular member. The chamber of the balloon communicates with the lumen of the inner tubular member by a channel which passes radially through the outer tube member, the tubular sleeve, and the inner tubular member. The cannula may have one or more ports either proximal or distal the balloon occluder and communicating with the lumen of the gap between the inner and outer tubular members.
The method for making nested tubing sections includes an initial step of heat-bonding a beading into the lumen of a tubular member which has a proximal end, a distal end, and a lumen therebetween, to seal the distal opening. A tubular sleeve is heat-bonded circumferentially about the distal end of the tubular member. The tubular member is then nested within the lumen of a larger tubular member which has a proximal end, a distal end, and a lumen therebetween. The tubular sleeve may be aligned substantially with the distal end of the outer tubular member. The outer tubular member is then heat-bonded to the tubular sleeve. A channel is created through the outer tubular member, the tubular sleeve, and inner tubular member, the channel communicating with the lumen of the inner tubular member. Another channel or channels are created through the outer tubular member and are in communication with the lumen disposed between the inner and the outer tubular members. In an alternative embodiment where the distal end of the cannula is angulated relative to its proximal end, heat is applied to bend the distal end of the cannula.
It will be understood that there are many advantages to creating nested tubing sections disclosed herein. This invention does not require expensive tooling, but simply utilizes multiple tubes that are nested together and bonded. Internal inserts may be formed into the tubes at varying layers. In addition, varying materials having different physical properties, such as hardness, flexibility, color and melting temperature, may be incorporated to improve desired performance characteristics. For example, a low melting temperature outer tube, a rigid center tube and soft inner tube can be combined to create a rigid, soft tip, heat-bondable tube.